Rapid Production of High‐Purity Hydrogen Fuel through Microwave‐Promoted Deep Catalytic Dehydrogenation of Liquid Alkanes with Abundant Metals

Hydrogen as an energy carrier promises a sustainable energy revolution. However, one of the greatest challenges for any future hydrogen economy is the necessity for large scale hydrogen production not involving concurrent CO₂ production. The high intrinsic hydrogen content of liquid‐range alkane hydrocarbons (including diesel) offers a potential route to CO₂‐free hydrogen production through their catalytic deep dehydrogenation. We report here a means of rapidly liberating high‐purity hydrogen by microwave‐promoted catalytic dehydrogenation of liquid alkanes using Fe and Ni particles supported on silicon carbide. A H₂ production selectivity from all evolved gases of some 98 %, is achieved with less than a fraction of a percent of adventitious CO and CO₂. The major co‐product is solid, elemental carbon.     

Identifying Different Types of Catalysts for CO2 Reduction by Ethane through Dry Reforming and Oxidative Dehydrogenation

The recent shale gas boom combined with the requirement to reduce atmospheric CO₂ have created an opportunity for using both raw materials (shale gas and CO₂) in a single process. Shale gas is primarily made up of methane, but ethane comprises about 10 % and reserves are underutilized. Two routes have been investigated by combining ethane decomposition with CO₂ reduction to produce products of higher value. The first reaction is ethane dry reforming which produces synthesis gas (CO+H₂). The second route is oxidative dehydrogenation which produces ethylene using CO₂ as a soft oxidant. The results of this study indicate that the Pt/CeO₂ catalyst shows promise for the production of synthesis gas, while Mo₂C‐based materials preserve the C? C bond of ethane to produce ethylene. These findings are supported by density functional theory (DFT) calculations and X‐ray absorption near‐edge spectroscopy (XANES) characterization of the catalysts under in situ reaction conditions.     

Simultaneous propane dehydrogenation andco2hydrogenation overCrOx/SiO2catalyst

Summary Single reverse water-gas shift (RWGS) and dehydrogenation of propane with CO₂(DH-CO₂) reactions in the presence and absence of the CrO_x/SiO₂ catalyst have been studied between 673 and 873 K. It was found that the CrO_x/SiO₂ catalyst is active both in the dehydrogenation of propane and in the RWGS reactions. The obtained results suggest that the dehydrogenation of propane to propene in the presence of CO₂on CrO_x/SiO₂can be facilitated by the RWGS reaction.</o:p>     

Towards a Practical Development of Light‐Driven Acceptorless Alkane Dehydrogenation

The efficient catalytic dehydrogenation of alkanes to olefins is one of the most investigated reactions in organic synthesis. In the coming years, an increased supply of shorter‐chain alkanes from natural and shale gas will offer new opportunities for inexpensive carbon feedstock through such dehydrogenation processes. Existing methods for alkane dehydrogenation using heterogeneous catalysts require harsh reaction conditions and have a lack of selectivity, whereas homogeneous catalysis methods result in significant waste generation. A strong need exists for atom‐efficient alkane dehydrogenations on a useful scale. Herein, we have developed improved acceptorless catalytic systems under optimal light transmittance conditions using trans‐[Rh(PMe₃)₂(CO)Cl] as the catalyst with different additives. Unprecedented catalyst turnover numbers are obtained for the dehydrogenation of cyclic and linear (from C₄) alkanes and liquid organic hydrogen carriers. These reactions proceed with unique conversion, thereby providing a basis for practical alkane dehydrogenations.     

Autocatalytic dehydrogenation of propane

Homogeneous gas-phase pyrolysis of propane was performed by using continuous CO₂ laser irradiation for bulk heating of the reaction mixture. Laser energy was absorbed by ethylene, the main product of propane dehydrogenation, and transferred to the reaction medium via collisional relaxation. A mechanism of propane dehydrogenation is suggested to describe the pyrolysis process. The mechanism involves autocatalysis by ethylene and includes propane–ethylene interaction with the formation of ethyl and propyl radicals.     

Modeling CO2 electrolysis in solid oxide electrolysis cell

A modified Butler–Volmer equation for the reduction of CO₂ by considering multi-step single-electron transfer reactions is presented. Exchange current density formulations free from arbitrary order dependency on the partial pressures of reactants and products are proposed for Ni and Pt surfaces. Button cell simulations are performed for Ni-YSZ/YSZ/LSM, Pt-YSZ/YSZ/Pt, and Pt/YSZ/Pt systems using two different electrochemical models, and simulation results are compared against experimental observations. The first electrochemical model considers charge transfer reactions occurring at the interface between the electrode and dense electrolyte, and the second model considers the charge transfer reactions occurring throughout the thickness of the cermet electrode. Single-channel simulations are further performed to asses the O₂ production capacity of CO₂ electrolysis system.     

Hybrid direct carbon fuel cells and their reaction mechanisms—a review

As coal is expected to continue to dominate power generation demands worldwide, it is advisable to pursue the development of more efficient coal power generation technologies. Fuel cells show a much higher fuel utilization efficiency, emit fewer pollutants (NO _x , SO _x ), and are more easily combined with carbon capture and storage (CCS) due to the high purity of CO₂ emitted in the exhaust gas. Direct carbon (or coal) fuel cells (DCFCs) are directly fed with solid carbon to the anode chamber. The fuel cell converts the carbon at the anode and the oxygen at the cathode into electricity, heat and reaction products. The use of an external gasifier and a fuel cell operating on syngas (e.g. integrated gasification fuel cells) is briefly discussed for comparative purposes. A wide array of DCFC types have been investigated over the last 20 years. Here, the diversity of pre-commercialization DCFC research efforts is discussed on the fuel cell stack and system levels. The range of DCFC types can be roughly broken down into four fuel cell types: aqueous hydroxide, molten hydroxide, molten carbonate and solid oxide fuel cells. Emphasis is placed on the electrochemical reactions occurring at the anode and the proposed mechanism(s) of these reactions for molten carbonate, solid oxide and hybrid direct carbon fuel cells. Additionally, the criteria of choosing the ‘best’ DCFC technology is explored, including system design (continuous supply of solid fuel), performance (power density, efficiency), environmental burden (fresh water consumed, solid waste produced, CO₂ emitted, ease of combination with CCS) and economics (levelized cost of electricity).     

Methane Activation by Diatomic Molybdenum Carbide Cations

Metal carbide species have been proposed as a new type of chemical entity to activate methane in both gas‐phase and condensed‐phase studies. Herein, methane activation by the diatomic cation MoC⁺ is presented. MoC⁺ ions have been prepared and mass‐selected by a quadrupole mass filter and then allowed to interact with methane in a hexapole reaction cell. The reactant and product ions have been detected by a reflectron time‐of‐flight mass spectrometer. Bare metal Mo⁺ and MoC₂H₂⁺ ions have been observed as products, suggesting the occurrence of ethylene elimination and dehydrogenation reactions. The branching ratio of the C₂H₄ elimination channel is much larger than that of the dehydrogenation channel. Density functional theory calculations have been performed to explore in detail the mechanism of the reaction of MoC⁺ with CH₄. The computed results indicate that the ethylene elimination process involves the occurrence of spin conversions in the C?C coupling (doublet→quartet) and hydrogen atom transfer (quartet→sextet) steps. The carbon atom in MoC⁺ plays a key role in methane activation because it becomes sp³ hybridized in the initial stages of the ethylene elimination reaction, which leads to much lower energy barriers and more stable intermediates. This study provides insights into the C?H bond activation and C?C coupling involved in methane transformation over molybdenum carbide‐based catalysts.     

Statu quo sur la méthanation du dioxyde de carbone : une revue de la littérature

This review summarizes the statu quo and the perspectives of chemical methanation. CO₂ methanation, including catalyst deactivation, reactors, mechanisms, and thermodynamics are presented. This reaction serves as a test bed for our fundamental understanding of heterogeneous catalysis and is used in various industrial processes, including the removal of oxo-compounds (CO_x) in the feed gas for the ammonia synthesis, in connection with the gasification of coal, where it can be used to produce methane from synthesis gas, and in relation to Fischer–Tropsch's synthesis. Moreover, CO₂ methanation became of interest as a renewable energy storage system based on a “power-to-gas” conversion process by SNG (synthetic natural gas) production integrating water electrolysis and CO₂ methanation as a highly effective way to store the energy produced by renewables sources. The effectiveness and efficiency of the “power-to-gas” plants strongly depends on the CO₂-methanation process.     

Isobutanol dehydrogenation on copper-containing bismuth vanadates

It is found that α, β, and Γ modifications of perovskites Bi₄V_{2 ? 2x} Cu_2x O_{11 ? δ} (BICUVOX) exhibit different activities during catalytic transformations of isobutanol with a selectivity of isobutanal formation 85–100%. Data analysis shows that the site for the alcohol dehydrogenation reaction is the ion pair Cu²⁺-O^2? with the highest activity for a highly conductive γ-phase. It is shown that the activation energy for aldehyde formation is lower for γ-phase of the catalyst by a factor of ten than that for its α-phase. It is concluded that step-wise Arrhenius dependences without changes in the activation energy for parallel alcohol dehydrogenation and dehydration reactions are related to changes in the conducting properties of the catalyst. Step change in activity was found at temperatures of 310 and 370° and corresponds to an increase of the solid solution electric conductivity.     

Methanol transformations on framework lithium zirconium vanadate phosphates

The catalytic activity of framework phosphates of the general formula LiZr₂(VO₄)_x(PO₄)_3–x with different degrees of phosphorus replacement (x = 0, 0.1, 0.3, 0.4, 0.6, and 0.8) was studied in methanol transformations in an inert atmosphere. It was shown that the ratio between the activity and selectivity of the catalysts in dehydration and dehydrogenation reactions is determined by their vanadium content and the process temperature.     

Effect of methane co-feeding on the selectivity of ethylene produced from oxidative dehydrogenation of ethane with CO2 over a Ni-La/SiO2 catalyst

A Ni-La/SiO₂ catalyst was prepared through the incipient wetness impregnation method and tested in the oxidative dehydrogenation of ethane (ODHE) with CO₂. The fresh and used catalysts were characterized by XRD and SEM techniques. The Ni-La/SiO₂ catalyst exhibited catalytic activity for the oxidative dehydrogenation of ethane, but with low ethylene selectivity in the absence of methane. The selectivity to ethylene increased with increasing molar ratio of methane in the feed. The carbon deposited on the catalyst surface in the sole ODHE with CO₂ was mainly inert carbon, while much more filamentous carbon was formed in the presence of methane. The filamentous carbon was easy to be removed by CO₂, which might play a role in improving the conversion of ethane to ethylene. The introduction of methane might affect the equilibrium of the CO₂ reforming of ethane and the ODHE with CO₂. As a consequence, the synthesis gas produced from CO₂ reforming of methane partly inhibited the reaction of ethane and promoted the ODHE with CO₂, thus increasing the selectivity of ethylene.     

Coverage-Dependent Behaviors of Vanadium Oxides for Chemical Looping Oxidative Dehydrogenation

Chemical looping provides an energy- and cost-effective route for alkane utilization. However, there is considerable CO₂ co-production caused by kinetically mismatched O²⁻ bulk diffusion and surface reaction in current chemical looping oxidative dehydrogenation systems, rendering a decreased olefin productivity. Sub-monolayer or monolayer vanadia nanostructures are successfully constructed to suppress CO₂ production in oxidative dehydrogenation of propane by evading the interference of O²⁻ bulk diffusion (monolayer versus multi-layers). The highly dispersed vanadia nanostructures on titanium dioxide support showed over 90 % propylene selectivity at 500 °C, exhibiting turnover frequency of 1.9×10⁻² s⁻¹, which is over 20 times greater than that of conventional crystalline V₂O₅. Combining in situ spectroscopic characterizations and DFT calculations, we reveal the loading–reaction barrier relationship through the vanadia/titanium interfacial interaction.     

Microfluidic Studies of Carbon Dioxide

Carbon dioxide (CO₂) sequestration, storage and recycling will greatly benefit from comprehensive studies of physical and chemical gas–liquid processes involving CO₂. Over the past five years, microfluidics emerged as a valuable tool in CO₂‐related research, due to superior mass and heat transfer, reduced axial dispersion, well‐defined gas–liquid interfacial areas and the ability to vary reagent concentrations in a high‐throughput manner. This Minireview highlights recent progress in microfluidic studies of CO₂‐related processes, including dissolution of CO₂ in physical solvents, CO₂ reactions, the utilization of CO₂ in materials science, and the use of supercritical CO₂ as a “green” solvent.     

Solubility of semi-fluorinated and nonfluorinated alkyl dichlorobenzoates in supercritical CO2

Isopleths and solution densities, from ∼25 to 100 °C, are reported for mixtures of CO₂ with semi-fluorinated and nonfluorinated propyl, butyl, octyl, and decyl 2,5-dichlorobenzoates. The maxima in the pressure–composition (P–x) isotherms for the alkyl 2,5-dichlorobenzoates range from 70 to 600 bar and the maxima increase with increasing alkyl chain length at each temperature. When the alkyl side chains are semi-fluorinated, the P–x maxima range from 60 to 175 bar over the same temperature range as with the nonfluorinated analogs. The P–x maxima of the semi-fluorinated 2,5-dichlorobenzoates in CO₂, first decrease as the benzoate alkyl chain is increased from propyl to butyl, but then increase as the alkyl chain length is further increased from butyl to octyl to decyl, although the differences in the maxima at a given temperature between these four semi-fluorinated benzoates are not as great as that observed with the nonfluorinated analogs. Also, the alkyl 2,5-dichlorobenzoate–CO₂ mixtures exhibit three-phase, liquid–liquid–vapor (LLV), equilibria near the vapor pressure curve and critical point of CO₂ whereas three phases are not observed for the semi-fluorinated analogs.     

Hydrogenation of CO2 Promoted by Silicon-Activated H2S: Origin and Implications

Unlike the usual method of CO_x (x = 1, 2) hydrogenation using H₂ directly, H₂S and HSiSH (silicon-activated H₂S) were selected as alternative hydrogen sources in this study for the CO_x hydrogenation reactions. Our results suggest that it is kinetically infeasible for hydrogen in the form of H₂S to transfer to CO_x at low temperatures. However, when HSiSH is employed instead, the title reaction can be achieved. For this approach, the activation of CO₂ is initiated by its interaction with the HSiSH molecule, a reactive species with both a hydridic H^δ− and protonic H^δ+. These active hydrogens are responsible for the successive C-end and O-end activations of CO₂ and hence the final product (HCOOH). This finding represents a good example of an indirect hydrogen source used in CO₂ hydrogenation through reactivity tuned by silicon incorporation, and thus the underlying mechanism will be valuable for the design of similar reactions.     

Mass spectrometric and thermal analyses of the salt system Zn<Subscript>2</Subscript>(OH)<Subscript>2</Subscript>CO<Subscript>3</Subscript> · <Emphasis Type="Italic">x</Emphasis>H<Subscript>2</Subscript>O-NaCl

The gas phase over nanocomposites consisting of zinc carbonate hydroxide (ZCH) Zn₂(OH)₂CO₃ · xH₂O(x = 1, 3) dispersed in a NaCl matrix has been characterized by high-temperature mass spectrometry and on-line FTIR spectroscopy coupled with thermal analysis. Volatile zinc-sodium chloro complexes are in equilibrium with ZCH-rich nanocomposites at 20–700°C under mass spectrometric conditions. This is evidence that sodium chloride reacts readily with zinc oxide nanoparticles. The thermal events in the ZCH-NaCl (Li₂CO₃) system have been investigated by differential scanning calorimetry.     

Autocatalytic gas-phase dehydrogenation of ethane

Homogeneous gas-phase pyrolysis of ethane by continuous CO₂ laser irradiation was used in our experiments for bulk heating of the reaction mixture. Laser energy was absorbed by ethylene, the main product of ethane dehydrogenation, and transferred to the reaction medium via collisional relaxation. A mechanism of ethane dehydrogenation is suggested to describe the pyrolysis process. The mechanism is autocatalytic in respect of ethylene and includes ethane?Cethylene interaction with the formation of methyl and propyl radicals. Rate constants of elementary reactions, selectivity, and yields of pyrolysis products were determined. The composition of ethane dehydrogenation products determined in the experiments was substantially different from the calculated thermodynamic equilibrium composition.     

New catalysts of dry reforming of methane into synthesis gas

New catalysts have been developed for the production of synthesis gas via a resource-saving and environmentally friendly process—dry reforming of methane. The catalysts are fabricated from NdCaCo_1–xNi _x On precursors (x = 0, 0.2, 0.4, 0.6, 0.8, 1) synthesized by a ceramic method. According to X-ray powder diffraction, when reacting with an equimolar CH₄/CO₂ mixture at 800–900°С, the precursors are converted into a mixture of neodymium and calcium oxides and cobalt and nickel metals. The catalyst based on NdCaNiO _n at 850°С has ensured high conversions of methane (91%) and CO₂ (86%) at СО and hydrogen yields of 88 and 78%, respectively. At 940°С, the yield of CO is close to the quantitative one (97%).     

CO2选择氧化低碳烷烃的研究进展

本文以低碳烷烃的选择催化氧化反应为对象，对几种CO₂选择氧化低碳烷烃的反应工艺进行了归纳总结，重点分析讨论了催化氧化反应中CO₂作为氧化剂的作用机制，并提出了研究展望。